Recent vehicle signaling lights such as turn signaling lamps, DRL (Day Running Lamp), etc. to be disposed on both right and left end portions of the front and rear areas of a vehicle body have utilized light emitting diodes (LED) and the like light sources, as the LEDs have high light emission efficiency and long life while consuming less power.
The LEDs having the above-described advantageous effects and serving as a light source generally emit light with high directivity. To cope with this, such an LED can be used together with a light guiding lens having an incident surface and a light output surface. In this configuration, the light with high directivity can be first caused to enter into the light guiding lens, and the light output surface of the light guiding lens can be illuminated with the entering light, as if the entire surface thereof can emit light.
For example, Japanese Patent Application Laid-Open No. 2009-223196 (or US Patent Application Publication No. 2009/0237910A corresponding to the JP publication) has proposed an indicator device including an LED and a plate light guiding lens. In this indicator device, light emitted from the LED is caused to enter into the plate light guiding lens in a direction parallel to the plate surface of the light guiding lens and be guided therethrough to the light output surface, thereby outputting the light through the light output surface. This can illuminate the linear light output surface thereof with the light as if the entire linear surface can emit light.
various illumination devices including the aforementioned indicator device have been required to be thinned in recent years. In order to cope with this demand, however, there is a certain limit to decrease the thickness of the LED for this purpose. Accordingly, Japanese Patent Application Laid-Open No. 2006-093104 (or US Patent Application Publication No. 2006/062016A corresponding to the JP publication) has proposed an illumination device including an LED 110 and a thin plate light guide plate 101 constituting a light guiding lens 100 as illustrated in FIG. 1. In this illumination device, the thin light guide plate 101 includes a light incident portion 100A opposite to the LED 110 and a light output surface 100b on the opposite side, and the light incident portion 100A includes expanded portions 102 and 103 expanded in the plate thickness direction.
Here, the light incident portion 100A of the light guiding lens 100 can have an elliptical cross section having two focal points F1 and F2 on its optical axis x. The light incident portion 100A includes a light incident surface 100a opposite to the LED 110 and disposed between the focal point F1 and the center of the ellipse. Light L1 emitted from the center of the LED 110 can be incident on the light incident surface 100a of the light guiding lens 100 while being refracted by the light incident surface 100a to enter the light incident portion 100A of the light guiding lens 100 illustrated as light L2. At that time, since the optical path through which the light L2 travels passes through the focal point F1 on the LED 110 side, the light L2 enters the light guiding lens 100 as if the light L2 has been emitted from the focal point F1. The light L2 having entered the light incident portion 100A is totally reflected off the surface of the expanded portion 102 (103) to become reflected light L3, which in turn passes through the focal point F2. Therefore, the light can effectively enter the light guide plate 101 after passing through the focal point F2.
The reflected light L3 enters the main portion of the light guide plate 101 to be light L4. The light L4 can be totally reflected by the inner surface of the light guide plate 101 repeatedly and guided toward the light output surface 100b (on the right side in FIG. 1). Finally, the light L4 can exit through the light output surface 100b, as if the entire light guiding lens 100 can emit light.
However, the light guiding lens 100 illustrated in FIG. 1 has the light incident portion 100A that is vertically symmetric in the thickness direction when seen as a cross section. In this case, the light having entered into the light guide plate 101 through the light incident portion 100A may be concentrated at a particular portion, so that point illumination may occur. As a result, the uniform illumination of the light output surface 100b cannot be achieved.